A seal cover (1) is provided for closing an opening portion (10) in a device in which a standby connector (11) is disposed. The standby connector (11) includes male terminals 11B for switching a state of an energizing circuit between a conductive state and a non-conductive state. Female terminals (23B), a shaft seal (25) and an O-ring (23D) are arranged in such a positional relationship that a time point when the shaft seal (25) is compressed maximally, a time point when the O-ring (23D) is compressed maximally and a time point when the female terminals (23B) are resiliently deformed maximally do not overlap with each other when the seal cover (1) is mounted on the opening portion (10).